Back in the late winter, early Spring (or possibly later than that...I'm about as good as a dog at gauging time passed) I opened up my garage to run the car and when I popped the hood I noticed a green droplet hanging from the rubber grommet connecting the right-side valve cover breather tube to the dual snorkel air cleaner assembly. When I took the lid off the air cleaner assembly I noticed a small amount of oil pooled inside my air cleaner that looked milky/cloudy. Also, when removing the cap from my radiator I noticed that my once full radiator was now roughly only 50-60% full.

Immediately fearing a blown head gasket I decided not to run the car and, as life got in the way, the car sat without running for a few months. Prior to spotting this, I drove the car as often as possible last year and never once had an issue with the car running rough, smoking badly, or over-heating. In fact it was the exact opposite - the car was running great as usual from what I could tell. On a few occasions while driving to local car shows, if I had a friend following behind me they would comment that the car blew a small amount of smoke from the exhaust when I would run the car a little hard, but I just chalked that up to blowing out the exhaust after letting the car sit for extended periods of time. The comments about light smoke from the exhaust mostly came after I had an issue where the points and condenser went bad while I was driving to a show, and the car back fired pretty loudly when that happened. Once I had the car towed home I had to start it up to get it into my garage and it was obviously running very rough and stalled several times while I was doing that but I had absolutely no other choice.

Now within the past week I started prepping to pull the heads but before I dove right in I checked a few simple things first:

- Spark Plugs are clean and dry
- Valve covers and the tops of the heads are spotless and what oil is still pooled on the top of the heads is normal, slightly dirty oil
- After draining the oil pan the oil is normal, slightly dirty oil that simply was due to be changed. No milky/cloudy appearance.

I also checked every square inch of the radiator and upper and lower hoses but see no signs of any kind of coolant leak. I even ran the car for several minutes to let it get hot and still no visible leaks and no smoky exhaust.

The ONLY thing I notice is that there is a small amount of smoke/steam coming from somewhere on the right side of the engine. It looks to be coming from in between the head and the exhaust manifold, close to the dipstick tube but it is really difficult to tell.

Also, it may be helpful to know that I likely have some blow-by from one of the right-side pistons because for the past couple years I have some oil that spits up through the breather tube into my air cleaner, but except for the one instance I noted above, the oil that blows into my air cleaner is always normal looking. I'm not saying this shouldn't have been addressed by now; I'm just trying to paint as complete a picture as possible for you.

Any ideas/thoughts/comments on where I could be losing coolant?

Sorry for the lengthy post and thank you in advance for helping!

Last edited by GeeTO400; 07-23-2018 at 08:49 PM.
Reason: Correcting a statement made in the original post

UPDATE: After topping off my radiator to the cold fill line, I pressure tested my cooling system and it held 15 lbs. of pressure for a solid two minutes without dropping any pressure.

So somehow my radiator lost roughly 1/4 to 1/2 it's volume of antifreeze but my cooling system doesn't have a leak, and the antifreeze isn't leaking into my oil. Also, there are no puddles on my garage floor.

I'm completely lost. Any more ideas where I could be losing antifreeze?

gmjunkie - Wow, sorry for not noticing your reply sooner, but thank you for asking. No, I never pulled the heads mainly because after some additional thought I decided that there was no need. I re-filled the radiator and drove the car several times without noticing any serious leaks; in fact after driving it several times there appeared to be no coolant loss at all now. There still seems to be some very minor coolant loss on occasion, but seeing as how there can't possibly be a serious issue (based on everything I have checked so far) I have just decided to stop worrying and enjoy driving my GTO.

Geeteeo400....That leak may be there. I am not trying to change your plans just a note to help you find the leak if it exists, or give even better piece of mind.

Here is the procedure, make sure you have a clean dry surface to park over, use a piece of cardboard under the car if you have to. on a cold engine put on your pressure tester. Warm up the car in the driveway to operating temp, pump up your tester to 15 lbs, put the car where you want it for the night, and shut it off. Make sure the pressure tester says 15 lbs and leave it. Have 2 beers and go to bed.

When you wake up go look under the car, you can do this in your onesie, but you may get some coolant on the feet.

If you have a coolant leak it will be obvious under the car. If no leak. You are good. If you see it trace it back and make the repair.

Now the another way is to put fluorescent in the coolant, they sell it in small bottles at all auto parts stores. You do not need to use the whole bottle, one little shot will color plenty. Do the same pressure test procedure, all night. If the leak is hard to take the dye helps find the source. You need a black light and glasses to see the dye.

Sometimes a small leak can be ez to fix a loose hose clamp, a pin pricked hose. Other times could be bigger issues, but this test will find the leak if there is a leak.

400 ......PS that is the test for an external leak,.....internal you have to check the oil for milky appearance, or white smoke from exhaust from
Coolant leaking head into the cylinder....you can put that combustion tester bulb into the radiator cap to see if byproducts of combustion are into coolant system...

But first go for the external leak procedure described above...you said the oil looked good..

Geeteeo400....That leak may be there. I am not trying to change your plans just a note to help you find the leak if it exists, or give even better piece of mind.

Here is the procedure, make sure you have a clean dry surface to park over, use a piece of cardboard under the car if you have to. on a cold engine put on your pressure tester. Warm up the car in the driveway to operating temp, pump up your tester to 15 lbs, put the car where you want it for the night, and shut it off. Make sure the pressure tester says 15 lbs and leave it. Have 2 beers and go to bed.

When you wake up go look under the car, you can do this in your onesie, but you may get some coolant on the feet.

If you have a coolant leak it will be obvious under the car. If no leak. You are good. If you see it trace it back and make the repair.

Now the another way is to put fluorescent in the coolant, they sell it in small bottles at all auto parts stores. You do not need to use the whole bottle, one little shot will color plenty. Do the same pressure test procedure, all night. If the leak is hard to take the dye helps find the source. You need a black light and glasses to see the dye.

Sometimes a small leak can be ez to fix a loose hose clamp, a pin pricked hose. Other times could be bigger issues, but this test will find the leak if there is a leak.

Good luck!

Good advice on the pressure testing. You can typically get one at your local parts store that offers free tool loaners. You simply put a deposit on the tool and when you bring it back, the will credit you your money - so no cost to you.

However, this may test for a leak using the pressure, but what it does not test is your radiator cap. Have had several caps go bad - rubber seal shrinks inside the underside of the cap or the pressure valve in the center has a rubber seal that can also go bad. The pressure valve can also weaken. So just a little enough can escape and then evaporates just as fast because the radiator is hot, so you never actually see the leak, but yet you can smell the anti-freeze.

I would install a new cap and/or check the one you presently have to make sure the cap is correct and seals match the neck on your radiator. The parts books at many stores sell generic one size fits all according to their computer screen when indeed, it is not a one size fits all situation. Made in China and the pressure cap may actually be lower than its rating and allowing pressure to escape.

As pointed out earlier, tighten all hose clamps. They can work just enough to be loose after they cycle a bunch of times - hot & cold. Make sure the clamp is correctly seated past the raised rib on most outlets, and not on the rib or before it. The clamp should be near the rib so as to squeeze the hose and take advantage of the rib to pinch the hose tight. I have been in a hurry and not paid attention where I placed the hose clamp, and sure enough, have just a tiny leak that like the radiator, I could smell the antifreeze, but not see it because it was vaporizing as it leaked out.

A bad heater core is another experience if it is still original. It'll leak/drip and evaporate. Then once you pull the heater core and inspect, sure enough, you can see the corrosion and leak stains.

Most of these cars have no overflow tank for the radiator. If you overfill the radiator, it will blow out a bit of coolant over time, and pull more coolant out in a syphon effect. Make sure your coolant is at least an inch below the filler neck, and make sure too pressure test your radiator cap, too. Many times weak caps are overlooked.